The research objective is to study the effects of ischemia on tissues distal to an applied tourniquet. Skeletal-muscle ischemia will be verified by measurements of blood flow and tissue p02 in the canine anterolateral muscle compartment. A minimum tourniquet pressure that provides a bloodless field will be determined. Loss of muscle and nerve function will be correlated with duration of tourniquet application. Necrosis in tissues distal to the tourniquet will be quantitated by recently-developed techniques for skeletal muscle. These basic correlates will be applied to the clinical use of tourniquets during limb surgery. Our previous studies of tissue fluid pressure and pressurization-time variables in the pathophysiology of the compartment syndrome indicate that skeletal-muscle necrosis can be quqntified by technetium-99 stannous pyrophosphate uptake, tissue calcium levels, plasma creatine phosphokinase and histological correlates. In addition, the irreversibility of the tissue necrosis can be determined by short- and long-term studies of muscle and nerve function in conjunction with histological evaluations. The toruniquet studies proposed here examine the effects of ischemic-term variables only. Along with studies of necrosis and function of post-ischemic tissue, all pressures governing tissue fluid balance will be followed directly by wick catheter, micropuncture, plasma osmometric and hollow-fiber membrane techniques. These investigations should provide sufficient data to determine a critical duration of ischemia which produces significant, irreversible necrosis in tissues distal to the tourniquet. At present, quantitative information regarding the effects of prolonged tourniquet application during limb surgery is lacking.